An automated fluorescence video system detected D. immitis microfilariae, tiny parasite forms measured in blood, more often than a standard manual wet mount in a laboratory comparison. At about 50 microfilariae per millilitre, it detected every tested positive sample, compared with 60% for the manual method. After a further twofold dilution, the automated method still recorded 100% sensitivity, while the wet mount fell to 10%.
The finding measures performance in prepared diluted samples, not across a broad population of naturally infected dogs. The evaluation used blood from one purpose-bred infected dog and one uninfected animal. Before dilution, the infected blood generally contained 30,000 to 60,000 microfilariae per millilitre.
A larger blood volume and automated scan
The study examined whether fluorescence videography combined with computer-vision analysis could detect and count D. immitis microfilariae in whole blood as an alternative to a standard wet mount. The manual comparison used a 20 microlitre drop examined at 100 times magnification. The automated system processed 1 millilitre of blood through a 5 micrometre mesh, added sodium fluorescein and recorded 15 frames at three frames per second for automated detection.
For the dilution and counting work, researchers examined five manual drops and five automated aliquots at each dilution. A separate high-dilution test used 10 repeats for each method at 1:500 and 1:1000, along with 10 uninfected aliquots. Storage-day comparisons used one-way analysis of variance, while count relationships were assessed with linear regression and fitted curves in Microsoft Excel.
Strong agreement across part of the range
Across seven dilutions from 1:5 to 1:100, manual counts followed a strong positive linear pattern. Automated counts followed a strong logarithmic pattern and began to level off between 1:40 and 1:20. The automated count was higher at every tested concentration. For the five highest dilutions, from 1:20 to 1:100, automated and manual counts showed a strong linear correlation, with a reported fit statistic of 0.9851.
The two methods produced counts on different scales. The reported regression slope was 13.2, and the authors interpreted this as more than 10 times as many automated counts as manual counts. They described an empirical conversion factor of 3.8 for turning a raw automated count into a wet-mount equivalent. The authors state that such factors require empirical recalibration if the system or method changes.
The test has unresolved boundaries
The automated method had a narrower useful range at high parasite burdens. Counts above 1,000 microfilariae per millilitre before treatment were described as insufficiently accurate. The authors estimated that about 20% of the microfilariae added to the mesh were detected and that only half of the surface was captured in full focus.
Both methods had 100% specificity in 10 counts of the negative sample. But the authors state that this figure referred to filarioids in general rather than D. immitis specifically. The study therefore does not establish that the system can distinguish D. immitis from D. repens.
In a six-day storage check, neither method showed an apparent change in counts, although the microfilariae appeared more lethargic by day six.
Questions the study leaves open
The study’s limited donor set means the result needs testing with more donors and naturally infected animals. Better focal coverage across the mesh and improved handling of high-burden samples are also needed before the system’s quantitative performance can be judged across a wider range.
The paper reports estimated US costs of US$20 to 30 for immunoassays, US$10 to 15 for clinical microscopy and under US$10 for the automated system. The figures were based in part on an assumed technician salary of US$30 and test times of 20 to 30 minutes.
The study was supported by Parasight System Inc. Its declaration lists several authors as full- or part-time Parasight employees and reports stock or stock options for some of them; two authors reported no competing interests. The article reports that it was received on 27 January 2026 and accepted on 21 May 2026.
Paper data and sources
Original title: Fluorescence videography for the rapid and automated in-clinic detection of microfilariae.
Authors: Britt Ripley, Mackenzie Smith, Alex Chen et al.
Journal/Repository: Parasites & vectors
Status: Peer-reviewed
First online: 2026-08-20
DOI: 10.1186/s13071-026-07486-y
Original paper · Full text